"We already knew it was a kind of gelatinous, soft animal," said marine biologist Rui Rosa of the University of Lisbon in Portugal, who led the study team.

The new data show "not an active or a fearsome predator, but one that has a really slow pace of life."

"Monster" Squid Ambushes Prey

Colossal squid are the world's largest invertebrates, or animals without backbones. The squid are shrouded in mystery: Colossal squid live in Antarctic waters at depths of about 6,560 feet (2,000 meters), and the elusive animals have never been observed alive in the wild.

For their new study, Rosa and colleagues looked at the physiologies and lifestyles of smaller, related squid species that also live in cold waters.

After scaling up the findings to match the colossal squid's size, the scientists concluded that the animal has a relatively low metabolic rate—in other words, colossal squid take a long time to convert nutrients from their food into energy.

This finding—plus the squid's cold blood and dark, icy home—implies that the colossal squid has generally slow movements and very low food requirements.

The team thinks the colossal squid ekes out an existence as a "sit and float" predator, grabbing the occasional passing fish, or by lying in ambush.

In fact, an 11-pound (5-kilogram) toothfish—known to be a typical meal for colossal squid—could sustain a 1,100-pound (500-kilogram) adult for 200 days, the study team estimates.

"It doesn't really have to consume much prey to maintain its way of life," Rosa said.

Overall, the squid's energy requirements are 300 to 600 times lower than those of warm-blooded whales, the other top predators in Antarctic waters.

And since the squid probably doesn't actively hunt, Rosa added, its dinner plate-size eyes are likely an adaptation for avoiding predators, such as sperm whales and sleeper sharks.